The present invention relates to a method of the type as stated in claim 1. In particular the method relates to the dividing of logs of wood into parts in order to obtain timber with vertical annual rings.
The invention has occurred during development work on the method which is described in SE 9100830. According to this method the log is first divided with at least two parallel longitudinal cuts which are substantially diametrical and parallel to the pith. Thereby at least one diametrical and plane parallel slab of wood is obtained which in its middle has a part made of the pith of the log. Furthermore a pair of essentially half logs are obtained. Further planks with vertical annual rings are obtained out of these through cutting with substantially radial cuts at an angel towards the pith. There remain pieces of wood with triangular cross-sections which can be glued together in the longitudinal direction with the triangular points pointing in opposite directions for adjacent pairs of pieces of wood in order to make a block with an even thickness and straight edges. Several blocks can be glued together to form thicker blocks which can be used as starting material for further manufacturing of wooden goods. This method gives an extremely high yield from the log and good quality of the finished timber.
The cut or cuts which are substantially diametrical and parallel to the pith give plane parallel slabs of wood which in their middles contain the pith of the log. The pith part in a log is of bad quality and therefore can not be used in timber. It is therefore cut away. The pith part in a log is considerably wider at the base of the log near its root. Therefore previously either a large part of the lower end of the log has been cut off or a large part of the middle of the slab or slabs of timber have been cut away after the initial cross cut sawing.
An object with the invention is to achieve an even better yield from a log and an even better quality of the timber after dividing into pieces.
Another object with the invention is to provide a way of working for cutting into pieces which requires so few operations as possible and which preferably can be controlled remotely.
Yet another object with the invention is to provide a system for dividing logs into pieces which gives low labour costs and/or low investment costs.
The above mentioned objects are achieved with a method which has the characteristics stated in claim 1. Further characteristics and further developments are mentioned in the other claims.
According to the invention the log is first cut into parts by a band or circular saw with at least two nearly diametrical cuts where the outmost lie symmetrically around the pith of the log. Each so obtained wide central plank is divided up through a pith cut so that two radial planks are obtained. Each radial plank is edged with the outer side as a reference for lining up and such that its edges become substantially parallel. In this way the influence of that the pith of the log is wider in the root part is avoided and each plank has good quality.
At the same time as the nearly diametrical cuts, the outermost part of each side of the log can be cut off with alignment cuts which are parallel with the nearly diametrical cuts. This is done so that the cuts lie so close to the edges as possible at the top end of the log. In this way a later shoulder is obtained which is wider at the root end of the approximately cone shaped blocks obtained on each side of the middle plank.
Each approximately conical block with the alignment cut is guided further through a twin-bladed saw, the cuts of which slant at 30xc2x0 towards the base surface of the block, and which cuts essentially radially symmetrically around the pith layer. The remaining part can then be turned the other way round and be cut by the same twin-blades saw in the same way. The two so obtained planks are edged. Alternatively, the log can be guided through two-twin blades saws, one after the other, which lean at 30xc2x0 in opposite directions. These saws can be displaced a relatively small amount in relationship to each other, but they can also be placed in different saw units so that the log is first completely guided through the first saw and then afterwards sawn in the opposite direction in the other saw.
The middle plank gives boards of good quality because the pith wood has been cut away.
A saw line in accordance with the invention in a basic embodiment can be equipped with machines which can be managed by four men. It gives a high yield of timber. Through remote controlling the output in a conventional way via for example TV cameras, the saw line can be handled by as few as two or three men which gives a high productivity of sales value per employee, considerably higher than in systems which were known before the invention.